Non-aqueous secondary batteries, such as lithium ion secondary batteries, have been widely used as power supply for portable electronic devices such as lap-top computers, mobile phones, digital cameras, and camcorders. Further, in recent years, since these batteries have a high energy density, application of these batteries to automobiles and the like has also been studied.
In conjunction with reductions in size and weight of portable electronic devices, the outer casing of a non-aqueous secondary batteries has been simplified. Recently, as the outer casing, a battery can made of an aluminum can has been developed in place of the battery can made of stainless steel that was previously used, and further, currently, a soft pack outer casing made of an aluminum laminate pack has been developed.
In the case of a soft pack outer casing made of aluminum laminate, since the outer casing is soft, a space may form between an electrode and a separator in conjunction with charging and discharging. This is one of factors contributing to deterioration of the cycle life, and therefore, uniform retention of the adhesive property of adhered portions of electrodes, separators, or the like is one of important technical problems.
As techniques relating to the adhesive property, various techniques for improving the adhesive property between an electrode and a separator have been proposed. As one of such techniques, a technique of using a separator in which an adhesive porous layer using a polyvinylidene fluoride resin is formed on a polyolefin microporous membrane, a conventional separator, has been proposed (see, for example, Patent Documents 1 to 3). The adhesive porous layer using a polyvinylidene fluoride resin functions as an adhesive that favorably joins the electrode and the separator together, when such an adhesive porous layer and an electrode are disposed adjacently in layers and subjected to compression bonding or heat pressing in a state in which an electrolyte is contained therein. Accordingly, the porous layer contributes to improvement of the cycle life of a soft pack battery.
As described above, in a separator having a polyolefin microporous membrane and an adhesive porous layer formed thereon, from the viewpoint of achieving both ion permeability and ensuring sufficient adhesive property, a new technical proposal focusing upon the porous structure and thickness of a polyvinylidene fluoride resin layer, and a new technical proposal that uses two kinds of polyvinylidene fluoride resins in combination, have been made.
Further, from the viewpoint of ensuring adhesive property, studies on polyvinylidene fluoride resins have been made, and appropriate coating amounts and compositions have also been proposed (see, for example, Patent Documents 4 to 7).
Meanwhile, in the process of producing a battery, it is known that the handling property of a separator has a great influence on the process yield at the time of production of a battery, and a technique of forming a lubricating layer, that is formed of a filler, on a separator surface to improve the slipping property has been proposed (see, for example, Patent Document 8).    Patent Document 1: Japanese Patent No. 4127989    Patent Document 2: Japanese Patent Application Laid-Open (JP-A) No. 2009-70609    Patent Document 3: JP-A No. 2003-77545    Patent Document 4: JP-A No. H11-260341    Patent Document 5: Japanese Patent No. 3225864    Patent Document 6: Japanese Patent No. 3225867    Patent Document 7: Japanese Patent No. 3225871    Patent Document 8: JP-A No. 2010-244875